This invention relates to the field of air cleaners and particularly to two-stage air cleaners which include a first, centrifugal cleaning stage, for removing larger particles, and a second, filtering stage, in which the filtering means includes an outer, principal filter enclosing an inner, "safety" filter. In such cleaners the principal factor determining the pressure drop across the cleaner is the size of the outlet opening. Since this opening can be no larger than the size of the smallest component of the filtering means, the desired low pressure drop must frequently be achieved at the cost of an increased size of the cleaner as a whole. This factor is further complicated by the fact that the effectiveness of the centrifugal cleaner stage is a function of the volume of air available outside the filtering means and near the collector for larger particles.